Methacrylate polymer concrete mix (MPC) has been employed to patch and repair concrete surfaces, such as roadways, sidewalks, runways and flooring. For example, MPC mix is described in British Pat. No. 983,826. To form a patch of cured MPC, methyl methacrylate monomer is mixed with a powder mixture and subsequently polymerized in situ after filling or covering the concrete area to be patched.
Once an initiator (usually a peroxide) and a promoter (usually an aromatic amine) have been added to the methacrylate monomer liquid polymerization takes place rapidly, in an hour or less in a typical case. For this reason it is a common practice to blend the promoter with the methacrylate monomer liquid and to blend the peroxide initiator with powder mixture, aggregate, and to combine the two blends at the repair site just prior to pouring the combined material into or onto the patch area. Alternatively, but less desirably, the powder mixture aggregate can be placed in or on the area to be repaired, and the peroxide initiator added to the liquid methacrylate monomer mixture which already contains the amine promoter, and this liquid mixture poured over the powder mixture so as to wet the particles.
The powder mixture is made of inorganic fillers such as silica or calcium carbonate of various particle sizes, colorants such as titanium dioxide and/or iron oxide, a polymerization initiator for methyl methacrylate monomer, a small amount of a plasticizer such as an organo-phosphate and a small amount of a methacrylate polymer. The methacrylate monomer portion (sometimes referred to hereinafter as liquid mixture) contains mostly methacrylate monomer along with a small amount of an anti-shrink agent such as a paraffinic oil and a small amount of a polymerization promoter such as N,N-dimethyl toluidine.
At the repair site, the powder mixture and the liquid mixture are combined, mixed, and poured onto the patch area. The polymerization initiator in the powder mixture initiates polymerization of the methacrylate monomer and the combined mixture, which is MPC, begins to cure through polymerization of the methacrylate. Upon completion of polymerization, the cured material is hard and concrete-like.
It is known that when the filler material of the powder mixture is of varying sizes, the spaces, or voids, between the particles is reduced. A filler, such as calcium carbonate, may also be a part of the powder mixture and aids in reducing the total void content. It is desirable to reduce the void content because, as the void content decreases, less monomer liquid is needed in the MPC. Less monomer liquid is desirable because the volume of the polymer formed is less than the volume of the corresponding monomer needed to form the polymer. Thus shrinkage occurs as the polymerization is carried out. Such shrinkage often causes cracking and delamination in the cured MPC. Thus, it is desirable to minimize the amount of monomer present.
However, as the amount of liquid is decreased, the combined powder mixture and liquid becomes stiff and difficult to work, such as by trowelling or smoothing, as it is placed and consolidated.